Scientists Detect Gravitational Waves for the Third Time

In the last months of 2015, a group of scientists shocked the world. Working at the twin detectors of the Laser Interferometer Gravitational Wave Observatory (LIGO), these researchers spotted gravitational waves for the first time in history. The LIGO team spotted gravitational waves again a few months later, and today the team has confirmed a third detection: a pair of colliding black holes, this time located about 3 billion light-years away. With this, LIGO is starting to create a new branch of science: gravitational wave astronomy.

Gravitational waves are ripples in the fabric of space-time caused by the movements of massive objects such as neutron stars and black holes. When these objects collide, they release immense energy in the form of gravitational waves, which stretch and compress space.

This stretching is tiny—millions of times smaller than an atom—which is why highly sophisticated detectors like LIGO are required to measure it. But ever since the first gravitational wave detection in 2015, LIGO has been in the perfect position to use these detections to learn more about the universe.

This most recent detection involved two black holes about 49 times the mass of our sun. The gravitational waves detected by LIGO formed when the black holes spiraled together and collided. The team also used the detection to study how the individual black holes were spinning.

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It turns out that as the black holes spiral together, they also spin, and the direction of that spin can tell us how they formed. If the black holes are both spinning in the same direction as the spiral—called "aligned" spin—then the black holes were most likely formed from a pair of stars that exploded at about the same time. If the black holes have any other kind of spin—called "non-aligned" spin—then they were most likely formed in different regions of their galaxy and just happened to come together. This is the type of spin that LIGO detected, which tells us something neat about the black holes we've spotted.

Currently, there are only two detectors that can spot gravitational waves: the two LIGO detectors in Louisiana and Washington state. But this summer a third detector will join the mix: the Virgo detector in Italy. With three detectors, gravitational wave astronomy is in position to reach for the stars.

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